international researchers said that sea level increases of 8 to 16 inches by 2050 could cause $60 billion to $63 billion in damages in 136 of the world’s coastal cities. That figure assumes the cities will undertake some flood control measures. Cities whose infrastructure and buildings are most at risk today — including New York City; New Orleans; Miami; Guangzhou, China; and Osaka, Japan — will be joined in another four decades by other rapidly growing cities, such as Ho Chi Minh City in Vietnam and Abidjan, Ivory Coast. “There is a pressing need to start planning how to manage flood risk now,” said Robert Nicholls, a professor of coastal engineering at the University of Southampton and a co-author of the study.